Fire resistant textile material

ABSTRACT

A fire resistant material comprising a woven faced fabric composed or fibres from meta-aramid, polyamideimide and mixtures thereof, the woven back fabric of low thermal shrinkage fibres selected from para-aramid, polyparaphenylene terephthalamide copolymer and mixtures there of.

This invention relates to fire resistant textile materials and garmentsmade from these materials. The invention relates particularly but notexclusively to articles of clothing for use by police, military, firefighters and for textiles for manufacture of such clothing. Europeanlegislation requires employers to provide garments which protect theiremployees against hazards to which they may be exposed. Clothing forprotection against heat and flame must pass minimum performancerequirements for flame, radiant heat, heat resistance, tensile and tearstrength, abrasion resistance and penetration by water and liquidchemicals. The assembled garments must achieve levels of resistance toheat transfer by both flame and radiant heat.

One of the most effective ways to reduce second and third degree bums isto make sure that the barrier of protective clothing between the heatsource and the skin remains intact during exposure and keep an air gapbetween the wearer and the heat source. This is referred to as the breakopen resistance or non-break open protection and active air entrapment.

An object of the present invention is to optimise thermal protectionoffered by the fabric. We have discovered that this can be achievedthrough use of enhanced fabrics design and fibre utilisation.

Outer textile materials for fire fighting clothing have previously beenmanufactured from 100% meta-aramid or polyamideimide blends ofmeta-aramid and para-aramid fibres or by use of core spun yarns orstaple mixtures with polyparaphenylene terephthalamide copolymer orfibres comprising para-aramid cores with meta-aramid or polyamideimidecovers. The combination of these fibres in the fabric enhances thenon-break open protection of the product. However meta-aramid andpolyamideimide fibres shrink, consolidate and thicken when exposed to ahigh temperature beat source. The presence of para-aramid orpolyphenylene terephthalamide copolymer in either the fibre blend or asa core can be used to prevent fibre shrinkage and consequent breakingopen of the garment. However the inclusion of para-aramid fibre in theblend has been found to be insufficient in tightly woven fabrics toprevent breaking open and does not increase the air gap between thewearer and the heat source. Consequently there is a need for improvedtextile materials for manufacture of fire fighting garments and thelike,

Fire fighting garments have been made from a plurality of textilelayers, including an outer layer of woven meta-aramid fibre, for exampleas manufactured under the trademark Nomex. Break open protection may beafforded by blending with para-aramid fibres, e.g. as manufactured underthe trademark Kevlar and as disclosed in U.S. Pat. No. 3,063,966 andU.S. Pat. No. 3,506,990. However charring of such blends may lead tocracking and embrittlement with consequent deterioration of physicalproperties.

PCT/GB00/01449 discloses a fire resistant textile material comprising awoven face fabric composed of fibres selected from meta-aramid,polyamideimide and mixtures thereof, the fabric including a woven meshof low thermal shrinkage fibres.

According to the present invention a method of manufacture of a fireresistant textile material comprising a woven faced fabric composed offace fibres selected from meta-aramid, polyamideimide and mixturesthereof the fabric including a woven back of low thermal shrinkagefibres, wherein the overfeed of the lower thermal shrinkage fibres isselected so that the sum of the extension under load and take-up isapproximately equal to the extension under load and take-up of the facefibres.

In a preferred embodiment the overfeed of the backing fibres is selectedso that the sum of the extension under load and take-up thereof isapproximately equal to the extension under load and take-up of the facefibres.

After exposure to a 10 second burn, the fabric of this invention hasbeen found not to break open whereas currently available fabricsmanufactured from a combination of these yarns fall apart under similarconditions. As there is higher shrinkage in the fibre on the surface ofthe fabric after thermal exposure than those on the back, the backfabric will buckle and there will be an increase the air gap between thelayers.

Meta-aramid fibres may have an extension including take-up of about 35%.Para-aramid used for the back yarns may have an extension includingtake-up of about 7%. Accordingly an overfeed in the region of 1.28, thatis a 28% overfeed may be employed in accordance with this invention.

Use of low thermal shrinkage fibres in accordance with the presentinvention increases the residual tensile strength of the textilematerial following exposure to flame or a radiant heat source. A lowthermal shrinkage fibre in accordance with this invention may be definedas a fibre which exhibits not more than 6% shrinkage when exposed to atemperature of 400° C. for a period of 5 seconds.

Low thermal shrinkage fibres in accordance with the present inventionmay be selected from the following materials:

polyparaphenylene terephthalamide (para-aramid e.g. Kevlar),polyparaphenylene terephthalamide copolymer, polyamideimide,copolyimide, phenolic fibres obtained by cross-linkage of phenolaldehyderesin and containing more than 70% carbon, polybenzimidazole,polyetheretherketone, high tenacity viscose, silicon carbide both with acore and with an organic precursor, ceramic fibres including alumina,alumina silicate and borosilico aluminate; and glass fibres including Eglass, C glass, D glass and R glass. Mixtures of the aforementionedfibres may be employed.

Preferred low shrinkage backing fibres are selected from para-aramid,polyparaphenylene terephthalamide copolymers; polyamideimide; carbonfibres and mixtures thereof.

Fibres or yams composed of 100% polyparaphenylene isophthalamidemeta-aramid (e.g. Nomex) shrink upon exposure to high temperatures, forexample in excess of 295° C. This shrinkage can result in shrinkage of awhole garment exposed to a flame. The low thermal shrinkage fibres, forexample para-aramid fibres or yams do not shrink to the same extent onexposure to this temperature. The thermal shrinkage of Kevlar is about3%, whilst the thermal shrinkage of Nomex is about 24%, If the twofibres or yams are combined in a fabric, the shrinkage of the fabric maybe controlled and/or restricted in such a way that the formation ofholes, or break opening, is minimised. The direction of the distortionof the fabric in the cross-sectional direction when exposed to a hightemperature may be controlled so that the fabric becomes thicker. Thiscontrol is achieved by use of a woven or warp knitted face fabric. Thisserves to increase the thermal protection afforded by the fabric andincreases the number of seconds needed to raise the temperature on theinner side to a level which would create pain or a second degree burn onhuman skin or on the type of sensor used in Thermal Protection Procedure(TPP) testing.

Fire resistant fabrics in accordance with this invention confer afurther advantage in comparison to fabrics composed of an intimate blendof meta-aramid and para-aramid fibres. Fabric formed from an intimateblend exhibits poor retention of the new appearance. The presence of lowthermal shrinkage fibres on the surface of a garment, for example Kevlarresults in formation of fine fibrils due to abrasion in use. Colouredfabrics, for example: dark blue as used for fire fighters' tunics maydevelop light specks on the surface of the fabric. This gives an unevenappearance an a dark coloured garment. The term used to describe thiseffect is fabric frosting.

The low shrinkage fibres are preferably disposed behind the face fabric.This minimises exposure of the strengthening fibres to the heat source.

Fabrics in accordance with the present invention also have the advantagethat degradation of the low thermal shrinkage fibres, which are moresusceptible to ultra-violet light degradation than other fibres, isreduced because they are not located on the outer surface of the fabric.

In preferred embodiments of the invention the low thermal shrinkagefibres form an interwoven backing fabric on the back of the face fabric.The low thermal shrinkage fibres preferably comprise para-aramid orpolyparaphenylene terephthalamide copolymer, e.g. Kevlar yarns. Thethickness of the yams may be selected in accordance with the resultantmass and weave of the finished fabric. The resultant mass (g/m²) willvary dependent on the particular end use but will generally be withinthe range 150 to 500 g/m².

The woven fabric is preferably a combination of a face fabric into whichis interwoven a backing fabric. The weave of the face fabric may varydependent upon the mass and end use required. The interweaving of thebacking scrim will be dependent on the weave of the face fabric and thethermal performance required.

In a preferred embodiment a true woven back is employed. For example thethickness may be generally doubled without an increase in weight. Thiscan result in improved thermal resistance. The air layer between thefront and back faces may protect the back layer under flame conditions.The Thermal Protective Performance (TPP) test as described below mayshow a 25% improvement in performance.

The textile material of this invention incorporating a woven back fabricmay be a double or multiple cloth, preferably a centre stitch, selfstitched or interchange double cloth. Internal stuffing yarns may beused to bulk out channels between the face and back fabrics.

In an especially preferred embodiment the textile material comprises acentre stitch double cloth. Preferably the backing fabric is overfed tocreate air spaces between the front and back layers. This may result ina pulled or corrugated appearance.

The extent of overfeed which may be used may be up to 35%, preferably upto 30%, more preferably in the range 25%. The extent of overfeed may beselected to balance the degrees of extension and load of the front andback axis. The extent of overfeed may be selected to give an optimum airlayer in order that the TPP value may be optimised for a particularapplication.

Fabrics in accordance with this invention may be produced byinterweaving yarns which have been spun and plied or core spun fromstaple fibres and/or multifilament fibres which may comprise 100%meta-aramid, 100% para-aramid, 100% polyamide imide or intimate blendsof any combination of these fibres.

The interweaving of the selected yarns may be such that a closely wovenfabric suitable for use as the outer face of a garment is combined witha loosely woven fabric which is suitable for use as the reverse side ofthe garment.

The selection of fibres and yarns which may be incorporated into fabricsin accordance with this invention will take account of the differentshrinkage properties of these fibres and the particular requirements ofthe final fabric. A combination of high and low shrinkage fibres may bechosen. For example meta-aramid face fabric with a thermal shrinkage ofapproximately 24% and a para-aramid backing fabric with a thermalshrinkage of approximately 3% may be employed.

The proportion and count of face side yarns to reverse side yarns may bedetermined by the required weight of the final fabric, the interlacingof the face weave and the degree of effectiveness required from theproperties of the reverse side yarn.

In a preferred embodiment the face yarns count may be in the range ofresultant 15 to 50 Nm (Numero metric, including single or multiplefolding of yarns), preferably 20 to 41 Nm. The reverse side yarns countmay be in the range 25 to 150 Nm, preferably 40 to 60 Nm (Numero metric,including single or multiple folding of yarns).

Independently the proportion or ratio of face to back yarns by numbermay be 1:2 to 20:1, preferably 1:1 to 4:1.

The interlacing of the face weave may be determined by the desiredappearance and the physical properties required of the final fabric.This interlacing may be any of a number of designs known to thoseskilled in the art. The preferred face weaves are plain weave, plainweave rip stop, twill weave rip stop or straight twill weaves and theirderivatives. FIG. 1 EX312 shows the weaving plan for a preferred fabric.Some other cloth and weave variations are:-

-   Self Stitched Double Cloths:--   Face weaves—1×1, 1×1 Rip Stop, 2×1 Twill, 2×1 Twill Rip stop and    their derivatives.-   Back weaves—1×1, 2×1 Twill and their derivatives.-   Centre Stitched Double Cloths (Centre stitching may be warp or weft    stitching or if both this then becomes a treble cloth):--   Face and Back weaves as for Self stitched cloths.-   Interchanged Double Cloths:--   Face and Back weaves would probably be the same to maintain a    regular face effect e.g. 1×1 or 2×1 Twill although they could be    different if required e.g. Face 2×1 Twill, Back 1×1, this would    however give a patterned effect.-   Cloths with Internal Stuffing Yarns:--   Face and Back weaves would probably be as for Self Stitched Cloths    with Stuffing Yarns laying between the two fabrics. The stuffing    yarns could be in warp, in weft or both.-   Multiple Cloths:--   These would combine more than two layers of fabric i.e. Triple    cloths, Quadruple cloths etc. Each layer of fabric could utilise    combinations of the weaves listed above.

Other weaves may be used if the requirements to do so arises. The degreeof interlacing between the face side yarns and the reverse side yarns isimportant to achieve a fabric which maximises the different propertiesof these yarns, gives a level surface and pleasing appearance and yetcan be woven with the highest possible efficiency.

In a preferred method the yarns for the warps of both the face andreverse sides of the fabric may be assembled in the specifiedproportions and order of working by the sectional warping process ontoone or two warped beams jointly having the total number of ends requiredto weave the final fabric.

The weft yarns may be inserted across and interlaced with the warp yarnsin the specified proportions, order of working and density selected toproduce the required face and reverse side weaves.

Differential tension may be applied to the face and reverse side yarnsduring the weaving process and during the insertion of the weft. This isimportant to compensate for the varying degrees of elongation which areinherent in the different types of fibres used in those yarns and whichare important to the properties of the fabric of this invention.

A preferred weaving machine which may be used to produce fabric of thisinvention is one that will supply the face and back warp yarns fromindividual warp beams at different fed rates to compensate for thevarying degrees of elongation and the varying inter-lacings of the facefabric yarns and reverse side yarns.

A preferred weaving machine should also have electronic filling centralbraking for independent weft, tensioning to compensate for the varyingdegrees of elongation and the varying inter-lacings of the face fabricyarns and reverse side yarns. The differential tensioning set to weavefabric of this invention may require a breaking force of 35% for theface yarn and 75% for the reverse side yarn.

Warp knitted fabrics may also be provided in accordance with thisinvention.

Previously known fire-fighting garments comprise a composite of threetextile layers, an outer fabric, a moisture barrier and a quiltedthermal lining. The present invention may reduce the need for use ofthree layers, or allow the total weight of those three layers to bereduced.

The invention is further described by means of example but not in anylimitative sense.

EXAMPLE 1

A textile material in accordance with the present invention (referred toin this specification as EX312) was woven using a self stitched doubleconstruction, with a blend of 93% meta-aramid, 5% para-aramid and 2%antistatic fibre (Nomex® Comfort) plain weave rip stop face and a 100%Kevlar back. It is woven in the proportions of two face to one backthread.

The overfeed of the para-aramid of 1.28, that is a 28% overfeed wasemployed.

Test Method

The fire resistance of textile materials in accordance with the presentinvention was determined using the following test method.

The Thermal Protective Performances of fabrics in accordance with thisinvention were measured by the Thermal Protective Performance (TPP)test. This test is a laboratory test to assess how well a fabric orcombinations of fabric provides a barrier to and insulation fromheat/flame.

In a “typical” flash fire the heat flux may be in the region of 80kW/m². The test method used a heat source with a heat flux of 80 kW/m²(2 cal/cm²/sec) made up of approximately 50% radiant and 50% convectiveheat exposed to the underside of the sample. Sensors are employed tomeasure a rise in temperature on the other side of the sample. This risein temperature is correlated, via earlier research work to the toleranceof human skin and susceptibility to pain and second degree bums as usedin TPP testing where “Stoll Curves” are used for the correlation. TheTPP test was used to measure heat energy required on outer surface(underside) of fabric or fabric combination to cause second degree burnsat the back of the fabric or fabric combination. The number of secondsrequired with a fixed level of energy (2 cal cm²sec⁻¹) to reach pain andsecond-degree burns is also determined. TABLE 1 Fabric & Description of2^(nd) degree TPP Fibre Fabric Assembly Pain (/sec) burn (sec) (Wcm⁻²)Factor EX312 (247 g/m²) 5.6 8.8 17.6 7.0 Total Weight: 247 g/m² NomexIII (265 g/m²) 4.6 7.5 14.9 5.6 Total Weight: 265 g/m²

The results are shown in Table 1. These indicated that the energyrequired to give second degree burns at the back of the fabric wasapproximately 25% higher for the textile material in accordance with thepresent invention referred to as quality EX312 than a fabric ofequivalent weight Nomex III fabric manufactured solely from the samefibres.

The thickness of EX312 fabric has increased from 0.7 mm before exposureto 4.3 mm after exposure, with air being trapped between the layers.This compares to the standard fabric increasing from 0.65 mm beforeexposure to 1.22 mm.

1. A method of manufacture of a fire resistant textile material comprising a woven faced fabric composed of face fibres selected from meta-aramid, polyamideimide and mixtures thereof the fabric including a woven back of low thermal shrinkage fibres, wherein the overfeed of the lower thermal shrinkage fibres is selected so that the sum of the extension under load and take-up is approximately equal to the extension under load and take-up of the face fibres.
 2. A textile material as claimed in claim 1, wherein the low thermal shrinkage fibres are selected from fibres having a shrinkage of less than 6% at 400° C.
 3. A textile material as claimed in claim 2, wherein the low them shrinkage fibres are selected from polyparaphenylene terephthalamide (para-aramid e.g. Kevlar), polyparaphenylene terephthalamide copolymer, polyamideimide, copolyimide, phenolic fibres obtained by cross-linkage of phenolaldehyde resin and containing more than 70% carbon, polybenzimidazole, polyethetetherketone, high tenacity viscose, silicon carbide bath with a core and with an organic precursor, ceramic fibres including alumina, alumina silicate and borosilico aluminate; and glass fibres including E glass, C glass, D glass and R glass and mixtures thereof.
 4. A textile material as claimed in any preceding claim wherein the low thermal shrinkage fibres are disposed behind the face fabric.
 5. A textile material as claimed in any preceding claim, wherein the low thermal shrinkage fibres form an interwoven backing fabric behind the face fabric.
 6. A textile material as claimed in any preceding claim, wherein the low thermal shrinkage fibres comprise para-aramid yarns.
 7. A textile material as claimed in any preceding claim, wherein the mass of the textile material is within the range 150 to 500 g/m².
 8. A textile material as claimed in any preceding claim, wherein the woven fabric is a combination of a face weave on which a backing fabric is interwoven.
 9. A woven textile material as claimed in any preceding claim, wherein the face yarns count is in the range of resultant 15 to 50 Nm.
 10. A woven textile material as claimed in claim 9, wherein the face yarns count is in the range of resultant 20 to 41 Nm.
 11. A woven textile material as claimed in claim 9 or 10, wherein the reverse side yarns count is in the range 5 to 150 Nm.
 12. A woven textile material as claimed in claim 11, wherein the reverse side yarns count is in the range 40 to 60 Nm.
 13. A woven textile material as claimed in any of claims 9 to 12, wherein the ratio of face to back yarns by number is in the range 1:1 to 20:1.
 14. A woven textile material as claimed in claim 13, wherein the ratio of face to back yarns by number is in the range 1:1 to 4:1.
 15. A woven textile material as claimed in any preceding claim, wherein the face weave is selected from: plain weave plain weave rip stops, straight twills, twill weave rip stops and their derivatives.
 16. A woven textile material where the thermal shrinkage of the face fibre is between 10 and 35%.
 17. A woven textile material where the thermal shrinkage of the back fabric is between 2 and 10%.
 18. A woven textile that increases in thickness between 2 and 10 times by differential shrinkage of fibre woven in the fabric, after exposure to a heat flux in excess of 40 KW/m².
 19. A woven textile that deforms to trap air in the fabric structure.
 20. A woven material that keeps 30% of its strength after exposure to 80 KW/m² of heat flux. 